Heterozygosity-fitness correlation at the major histocompatibility complex despite low variation in Alpine ibex (Capra ibex).

Alice Brambilla,Christine Grossen,Lukas Keller,Bruno Bassano

doi:10.1111/eva.12575

Abstract

Crucial for the long‐term survival of wild populations is their ability to fight diseases. Disease outbreaks can lead to severe population size reductions, which makes endangered and reintroduced species especially vulnerable. In vertebrates, the major histocompatibility complex (MHC) plays an important role in determining the immune response. Species that went through severe bottlenecks often show very low levels of genetic diversity at the MHC. Due to the known link between the MHC and immune response, such species are expected to be at particular risk in case of disease outbreaks. However, so far, only few studies have shown that low MHC diversity is correlated with increased disease susceptibility in species after severe bottlenecks. We investigated genetic variation at the MHC and its correlations with disease resistance and other fitness‐related traits in Alpine ibex (Capra ibex), a wild goat species that underwent a strong bottleneck in the last century and that is known to have extremely low genetic variability, both genome‐wide and at the MHC. We studied MHC variation in male ibex of Gran Paradiso National Park, the population used as a source for all postbottleneck reintroductions. We found that individual MHC heterozygosity (based on six microsatellites) was not correlated with genome‐wide neutral heterozygosity. MHC heterozygosity, but not genome‐wide heterozygosity, was positively correlated with resistance to infectious keratoconjunctivitis and with body mass. Our results show that genetic variation at the MHC plays an important role in disease resistance and, hence, should be taken into account for successfully managing species conservation.

Highlights

The ability to fight disease and to adapt to novel pathogens is crucial for population survival but knowledge about the exact mechanisms driving disease resistance in wild species is still limited (AcevedoWhitehouse & Cunningham, 2006; Buitkamp et al, 1996; Radwan et al, 2010; Spielman et al, 2004)
We studied major histocompatibility complex (MHC) variation in male ibex of Gran Paradiso National Park, the population used as a source for all postbottleneck reintroductions
The aims of this study were to precisely estimate the genetic variation at the MHC in the source of all existing Alpine ibex populations, the Gran Paradiso one, and to investigate whether individual variation at the MHC was correlated with disease susceptibility or other fitnessrelated traits

Summary

| INTRODUCTION

The ability to fight disease and to adapt to novel pathogens is crucial for population survival but knowledge about the exact mechanisms driving disease resistance in wild species is still limited (AcevedoWhitehouse & Cunningham, 2006; Buitkamp et al, 1996; Radwan et al, 2010; Spielman et al, 2004). The low diversity at the MHC observed in Alpine ibex could be one of the factors explaining disease susceptibility in this species It might be crucial for the conservation of this and of other bottlenecked species, the previous studies did not have access to individual-based fitness data including disease susceptibility. The aims of this study, conducted in the source of all existing Alpine ibex populations, were 1) to estimate genetic variation at the MHC region using more markers and a larger sample size than previous studies in the Gran Paradiso population and 2) to investigate whether variation at the MHC region (measured as multilocus heterozygosity or heterozygosity at single loci) is correlated with fitness-related traits and with resistance to infectious keratoconjunctivitis

| METHODS

| DISCUSSION

Findings

40 Hom Het Hom Het Hom Het Hom Het